The present invention relates to a droplet ejection apparatus and a droplet ejection head.
An electro-optic device, such as a liquid crystal display (LCD) device or an organic electroluminescence display device, normally includes a transparent glass substrate for displaying an image. An identification code (e.g., a two-dimensional code), which represents manufacturing information including for example a manufacturer or a product number, is marked on the substrate, and is used for quality management or manufacturing management of the electro-optic device. The identification code is formed by using an array of a plurality of pattern formation regions (cells). Some cells include code patterns (e.g., colored thin films or recessions), and other cells do not include code patterns. The manufacturing information is coded by including and excluding the code patterns from the cells.
As methods for forming the identification code, a laser sputtering method and a water jet method have been proposed (JP-A-11-77340 and JP-A-2003-127537). With the laser sputtering method, a metal foil is irradiated with a laser beam and sputtered to form the code patterns. With the water jet method, a jet of water containing abrasive material is ejected against a substrate to inscribe the substrate with the code patterns.
To obtain a code pattern of a desired size with the laser sputtering method, the distance between the metal foil and the substrate must be extremely short (e.g., less than 100 μm). Further, the surfaces of the substrate and the metal foil require flatness with high accuracy. This limits the kinds of substrates that can be used to form the identification codes. For this reason, the laser sputtering method has low versatility. With the water jet method, water, dust, and abrasive agent contaminate the substrate when the substrate is inscribed with the code patterns.
An inkjet method is recently receiving attention as a method to solve the above problems of the laser sputtering method and the water jet method. With the inkjet method, a functional liquid, in which metal particles are dispersed, is ejected as fine droplets onto a substrate, and the droplets on the substrate are dried to form the code patterns on the substrate. This method increases the kinds of substrates that can be used to form an identification code and avoids contamination of the substrate.
With the inkjet method, the code patterns are formed by drying blots of wet fine droplets that are deposited on or adhered to the substrate. This results in the problems that will now be discussed.
A blot of a fine droplet may spread out of a cell. A code pattern that includes a blot spread out from a cell may result in erroneous reading of the substrate information or disable the reading of substrate information.
This problem may be eliminated by irradiating blots of fine droplets with a laser beam to instantaneously dry the blots of the fine droplets. However, referring to FIG. 11, fine droplets Fb are ejected from an ejection head 90, which normally includes a passage 91 for a functional liquid F, a cavity 92 for storing the functional liquid F, and a pressurizing unit 93 for pressurizing the functional liquid F stored in the cavity 92. The layout and processing limitations limit the arrangement of a nozzle 94, which ejects a fine droplet Fb, to the middle portion of the ejection head 90.
More specifically, the position at which the fine droplet Fb is deposited (deposit position Pa) becomes farther from the position irradiated by a laser head 96 with a laser beam B (irradiation position Pb) as the nozzle 94 becomes closer to the middle of the ejection head 90. This delays the timing at which the fine droplet Fb is irradiated with the laser beam B by the time taken to move the fine droplet Fb, which is deposited at the deposit position Pa, to the irradiation position Pb. Thus, the drying of the fine droplet Fb is delayed, and the blot of the fine droplet Fb spreads out too much.
The timing at which the laser beam B is emitted may be expedited by emitting the laser beam B through a gap between a substrate 95 and the ejection head 90. However, the distance between the ejection head 90 and the substrate 95 is normally controlled to be in the order of millimeters to ensure the accuracy of the deposit position Pa. Thus, to emit the laser beam B to the blot of the fine droplet Fb through such a gap, the laser beam B needs to be emitted at an extremely acute angle. This may lower the accuracy of the irradiation position Pb, and may cause defective drying of the fine droplet Fb.